Products made from base webs such as bath tissues, facial tissues, paper towels, industrial wipers, foodservice wipers, napkins, medical pads, and other similar products are designed to include several important properties. For example, the products should have a soft feel and, for most applications, should be highly absorbent. The products should also have good stretch characteristics and should resist tearing. Further, the products should also have good strength characteristics, should be abrasion resistant, and should not deteriorate in the environment in which they are used.
In the past, many attempts have been made to enhance and increase certain physical properties of such products. Unfortunately, however, when steps are taken to increase one property of these products, other characteristics of the products may be adversely affected. For instance, the softness of nonwoven products, such as various paper products, can be increased by several different methods, such as by selecting a particular fiber type, by calendering, or by reducing cellulosic fiber bonding within the product. Increasing softness according to one of the above methods, however, may adversely affect the strength of the product. Conversely, steps normally taken to increase the strength of a fibrous web typically have an adverse impact upon the softness, the stiffness, or the absorbency of the web.
The present invention is directed to improvements in base webs and to improvements in processes for making the webs in a manner that optimizes the physical properties of the webs. In particular, the present invention is directed to a process for improving the tactile properties, such as softness and stiffness, of base webs without severely diminishing the strength of the webs.
In general, the present invention is directed to a creped web product having a unique fabric-imprinted pattern and a process for producing the product. The process of the present invention includes forming a base web, creping the base web in a manner known in the art, and then forming a unique, fabric imprinted pattern on at least one surface of the web at the same time as softening the web through a shear-inducing process.
To form the fabric imprinted pattern on the surface of the base web, the creped web is first placed between two moving conveyors. The conveyor/web sandwich thus produced is then guided around one or more compression inducing elements. As the conveyors are guided around the element(s), both shear forces and compressive forces are imparted to the web. The compressive forces can be such that a fabric imprinted pattern is formed on the surface of the base web while the shear forces can soften the web.
The compressive forces acting on the web can be greatest at those areas where the fabric knuckles of the conveyor contact the surface of the web. This can cause the fabric imprinted pattern formed on the web surface to be a series of high density troughs superimposed on the previously formed crepe pattern of the web. In an alternative embodiment, a fabric imprinted pattern can be formed on both surfaces of the web.
The compression inducing element can be any suitable element which can impart the necessary shear and compressive forces to the web. For instance, in one embodiment, the compression inducing element can comprise a roll having a small effective diameter of less than about ten inches. Particularly, the compression inducing element can have an effective diameter of less than about seven inches. More particularly, the compression inducing element can have and effective diameter of from about 2 to about 5 inches.
The web can be essentially dry when guided around the compression inducing element of the present invention. For example, the web can have a moisture content of less than about 10% by weight.
In order to suitably soften and form the pattern in the web, the conveyors should be under a tension when wrapped around the shear/compression inducing element. For example, the conveyors can be wrapped around the element at least 30xc2x0. More specifically, the conveyors can be wrapped around the element at least 50xc2x0. The conveyors can be under a tension of at least 5 pounds per linear inch when guided around the compression inducing element.
The unique creped web product of the present invention can be formed of any suitable base web. For example, the base web can have a basis weight between about 5 and about 40 grams per square meter. The paper product can be a single-ply product or a multi-ply product. Additionally, any single ply of the paper product can be a homogeneous or a stratified web. The creped paper product of the present invention can be formed of any suitable fiber type.
The paper product of the present invention is a soft, strong creped product which can exhibit limited caliper decrease during processing. For example, the paper product of the present invention can exhibit a geometric mean tensile strength of greater than about 200 grams per inch. More specifically, the paper product can exhibit a geometric mean tensile strength of greater than about 250 g/in. The bulk of the creped web product can be greater than that of other calendered tissue products. For example, the bulk can be greater than about 7.5 cc/gram. More specifically, the bulk can be greater than about 8.5 cc/gram.
Likewise, the caliper of the disclosed paper product can be greater than that of a similar calendered, creped web product. In one embodiment, the caliper can be greater than about 250 microns. More specifically, the caliper can be greater than about 275 microns.